av·e·nue (v-n, -ny)
n.
1. Abbr. Ave. or Av. A wide street or thoroughfare.
2.
a. A broad roadway lined with trees.
b. Chiefly British The drive leading from the main road up to a country house.
3. A means of access or approach: new avenues of trade.
http://www.thefreedictionary.com/avenue

planed or planted?

"Here" they say - do you mean the LEO dictionary?

@ penguin: here or there, doesn't matter ;) there would have been better probably ...

@ all:

so an avenue doesn't necessarily have trees;

but Allee means the road has trees, necessarily - so there is actually no English word for Allee ... ?

Yes there is. See above -- at least according to the dictionary definition.) It just has multiple meanings.

Sort of like trying to translate German's all-purpose "belasten." We have to use many different words to translate that idiomatically.

Updating a dictionary means being aware of emerging vocabulary and of changes in the way existing words are being used
It's not the job of a dictionary to tell you how to use a word but to report how it is being used....
http://www.macmillandictionary.com/love/steph...

Siehe Wörterbuch: avenue
Siehe Wörterbuch: Allee

... ist "alley" nicht eher ein (kleinerer) Durchgang ?

https://www.google.com/#q=definition%20boulevard

A boulevard usually has trees.

An alley is usually a small street that runs behind a building. It is generally used to make deliveries and pick up garbage. Most cities in American have them in the business district, though New York City is an exception to that.

I'd say that the "alley" translation for "Allee" is wrong (at least in AE in most contexts.)

"Boulevard" could also work for "Allee" (except in Chicago, where it refers to a larger street on which commercial vehicles are prohibited).

However, since neither "boulevards" nor "avenues" are necessarily tree-lined (in AE at least), the best solution is likely "a tree-lined XXX." We have to face reality, in both directions between English and German, there are many cases when there is no one-to-one translation.